Hong Kong police fired tear gas and rubber bullets at protesters who had massed outside government headquarters Wednesday in opposition to a proposed extradition bill that has become a lightning rod for concerns over greater Chinese control and erosion of civil liberties in the territory.

The afternoon violence marked a major escalation in the semiautonomous Chinese city's biggest political crisis in years. It came after protesters earlier in the day forced the delay of a legislative debate over the bill, which would allow criminal suspects in Hong Kong to be sent for trial in mainland China.

The overwhelmingly young crowd had overflowed onto a major downtown road as they overturned barriers and clashed with police outside the government building. But when some appeared to have breached the police cordon around the building, the police launched their response, which also included firing pepper spray and water hoses.

Earlier, a curt government statement said the legislative session scheduled to begin at 11 a.m. would be "changed to a later time." Officials gave no indication of when that would be and Hong Kong leader Carrie Lam canceled a scheduled news briefing.

The delay appeared to have been at least a temporary victory for the bill's opponents, whose protests are the largest since pro-democracy demonstrations closed down parts of the Asian financial center for more than three months in 2014. Some businesses closed for the day, and labor strikes and class boycotts were called.
The protests are a challenge to China's ruling Communist Party and President Xi Jinping, who has in the past said he would not tolerate Hong Kong being used as a base to challenge the party's authority. But they are also giving vent to young Hong Kong residents alienated by a political process dominated by the territory's economic elite.